Physical-chemical bases for improving strength of open-hearth bottoms during high speed repairs

Conclusions

The physical-chemical basis of high-speed methods of welding on hearths in open-hearth furnaces is intensification of the recrystallization of periclase brought about by high concentrations of iron oxides and high-temperature conditions.

An important condition for high speed surfacing methods is the use of scale which intensifies the periclase recrystallization over a relatively short surfacing time.

In high-speed methods of surfacing hearths with scale, the periclase recrystallization develops both in the grains as well as in individual fine periclase crystals (magnesiowustite) forming the binder in the hearth together with silicates and glass.

The reerystallization of the periclase in the grains (aggregates) and in the binder leads to the magnesiowustite crystals growing together, which increases the strength of the hearth; this is further improved by the increase in the amount of dicalcium silicate in the binder.

The strength of the hearth is improved by chromemagnesite powder (the magnesite part in the form of a dispersed fraction) through the formation of solid solutions of complex spinel in the periclase (the spinel evidently dissolves in the silicate melt more slowly) and the strong crystalline concretion of the former dispersed periclase grains in the binding component in the hearth. The use of fine grain metallurgical powder containing 20 – 25% fraction finer than 0.02 or 0.088 mm and a coarse fraction with 7 – 10 mm grains has a favorable effect.